Electrostatic proximity fuse

ABSTRACT

1. In combination with an explosive missile, an electrostatic fuse comprising: a conical casing mounted at the nose end of said missile, said casing having a metal cap at its narrow end and an insulating skirt between said cap and the body of said missile whereby a capacitance C exists between said cap and said body, said cap and said body having a charge placed thereon during missile launching; a resistance R connected between said cap and said body, said resistance R thereby being in parallel with the capacitance C, the value of said resistance R being such that the time constant RC is long compared to the time the missile is within proximity of a target, but short compared to the time of flight of the missile; a pentode mounted within said missile at its nose end, said pentode having an anode, a cathode, and three grids, the number 2 grid of said pentode being connected to said cap, and the number 1 and number 3 grids of said pentode being connected to said cathode, said cathode being connected to the body of said missile, said number 2 grid thereby being shielded from both said anode and said cathode; a positive voltage source within said missile; a resistor connected between the anode of said pentode and said source; a firing circuit having a thyratron, a charged capacitor, and a detonator, said thyratron having an anode, a cathode, and a grid, said charged capacitor and detonator being connected in the anode circuit of said thyratron; and a coupling network connected between the anode of said pentode and the grid of said thyratron; the greater increase in the capacitance of said cap than that of said body upon approach of said missile to a target causing a change in the voltage across said parallel capacitance C and resistance R, this voltage change being amplified by said pentode and transferred by said coupling network to the grid of said thyratron, whereupon said thyratron conducts causing said charged capacitor to pass a current through said detonator causing functioning thereof.

United States Patent Heilprin et al.

[451 Mar. 18, 1975 1 1 ELECTROSTATIC PROXIMITY FUSE [75} Inventors: Laurence B. Heilprin; George Nordquist; Philip Krupen, all of Washington, D.C.

[73] Assignee: The United States of America as represented by the Secretary of the Army, Washington, D.C.

{22] Filed: Mar. 26, I951 1211 Appl. No.: 217,652

OTH ER PU BLICATIONS "Proximity Fuzes for Artillery, Selvedge, Electronics, February, 1946, pp. l04109.

Primary ExaminerBenjamin A. Borchelt Assistant E.\aminerC. T. Jordan Allurney, Agent, or FirmNathan Edelberg; Robert P. Gibson; Saul Elbaum EXEMPLARY CLAIM l, in combination with an explosive missile, an electrostatic fuse comprising: a conical casing mounted at the nose end of said missile, said casing having a metal cap at its narrow end and an insulating skirt between said cap and the body of said missile whereby a capacitance C exists between said cap and said body, said cap and said body having a charge placed thereon during missile launching; a resistance R connected between said cap and said body, said resistance R thereby being in parallel with the capacitance C, the value of said resistance R being such that the time constant RC is long compared to the time the missile is within proximity of a target, but short compared to the time of flight of the missile; a pentode mounted within said missile at its nose end, said pentode having an anode, a cathode, and three grids, the number 2 grid of said pentode being connected to said cap, and the number 1 and number 3 grids of said pentode being connected to said cathode, said cathode being connected to the body of said missile, said number 2 grid thereby being shielded from bothsaid anode and said cathode; a positive voltage source within said missile; a resistor connected between the anode of said pentode and said source; a firing circuit having a thyratron, a charged capacitor, and a detonator, said thyratron having an anode, a cathode, and a grid, said charged capacitor and detonator being connected in the anode circuit of said thyratron; and a coupling network connected between the anode of said pentode and the grid of said thyratron; the greater increase in the capacitance of said cap than that of said body upon approach of said missile to a target causing a change in the voltage across said parallel capacitance C and resistance R, this voltage change being amplified by said pentode and transferred by said coupling network to the grid of said thyratron, whereupon said thyratron conducts causing said charged capacitor to pass a current through said detonator causing functioning thereof.

1 Claim, 3 Drawing Figures PATENTEB MARI 81975 INVENTORS Eeurge Nurdquiai LUUPETLEE B-Hei1prin Philip Krupen fammwpa ATTORNEYS U WMILH ELECTROSTATIC PROXIMITY FUSE This invention relates to proximity fuses and more particularly to an electrostatic proximity fuse.

An object of this invention is a proximity fuse that is substantially nonresponsive to jamming.

Another object of this invention is a nonradiating proximity fuse.

Another object of this invention is an electrostatic fuse that will not arm until the projectile has left the muzzle of the gun.

Another object of this invention is an electrostatic fuse, the functioning of which is dependent upon distortion of its electrostatic field as the projectile or missile in which the fuse is installed passes within relatively close proximity of the target.

Another object of the invention is to produce a type of proximity fuse which is simple and economical to manufacture.

The specific nature of this invention as well as other objects and advantages thereof will clearly appear from the following description and accompanying drawings in which:

FIG. I is a longitudinal sectional view showing one embodiment of the invention.

FIG. 2 is a block diagram illustrating the principles of operation of the electrostatic fuse.

FIG. 3 is a schematic diagram of the electrostatic fuse of the invention wherein filament-cathode type of tubes are employed.

Referring to the drawings by characters of reference, there is shown in FIG. I an embodiment of the invention wherein 1 indicates a mortar projectile having a windshield 2 comprising a metal cap 3 and a conically shaped shirt 4 of relatively high electrical resistance. The electronic components of the fuse are housed in the windshield which may be attached to the body la of the projectile by any one of the well known methods. The open end lb of the body la has fixed therein a booster 29 in intimate contact with an explosive charge 5. A detonator 6 is contained in the booster 29. The windshield has fixed therein two spaced partitions 7 and 8. An amplifier tube 9 and a thyratron 10 are mounted on the partition 7. Partitions 7 and 8 form a compartment 11 in which are suitably retained the resistances, capacitances and associated wiring of the fuse. Partition 8 forms with one face of the booster 29 a compartment 12 in which are mounted the switches, power supply and associated wiring of the fuse. The partitions 7 and 8 are held in spaced relation within the body 4 by means of spacers 13, I4 and 15 in a manner which can be easily ascertained by inspection of FIG. I.

The block diagram of FIG. 2 serves to generally illustrate the method of operation of the electrostatic fuse of this invention. The projectile l is charged by any suitable device such as a dust charger or by the ionized gases of the propelling charge as or after it leaves the muzzle of the projector or gun (not shown). The skirt 4 which joins and insulates the cap 3 from the body 1a forms part or all of resistor R which is shunted across the input of the vacuum tube amplifier. The value of the resistor R is such that the time constant of R and capacitance C. which exists between the cap 3 and the body la, which is parallel with R, is long compared to the time the projectile is within the proximity of the triggering target 16, but short compared to the time of flight of the projectile. Because the time constant RC is short as compared to the time of flight, the resistor R allows the cap 3 and body la to assume the same potential shortly after the projectile has left the muzzle. This condition continues until a target is approached. As the projectile comes within effective proximity of the target, significant changes in capacitances l7 and 18 occur between the cap 3 and the target, and the body 1a and the target respectively. Because the time constant RC is long as compared to the time the projectile is within effective target proximity, the charges on the cap 3 and the body la will remain essentially constant during this time. From well-known physics theory, a change in the capacitance of a body while its charge remains constant causes an inversely proportional change in the potential of the body. Therefore, the potentials on the body la and the cap 3 decrease at effective target proximity. Since the cap 3 is smaller in size than the body 1a and closer to the target, its increase in capacitance 18 will be much more pronounced than the corresponding increase in the capacitance 17. The potential of the cap 3 therefore will decrease considerably more than the potential on the body la. Target proximity thus causes a negative voltage differential between the cap 3 and the body 1a. This voltage differential is amplified by the amplifier which in turn triggers the thyratron to function the detonator.

In the diagram of FIG. 3 the amplifier and thyratron tubes are of the filament-cathode type and are coupled to each other by a conventional coupler 43. As shown, the amplifier tube 9 is a pentode having its number 2 grid connected to the cap 3 of the windshield and its number 1 grid connected to the positive side of the cathode forming a shield for the number 2 grid, thereby protecting it from action of cathode material emitted by the hot cathode. Reference character 3b indicates the lead from the tip 3 to the number 2 grid. A battery 44 supplies current to the anode of the amplifier tube 9 through resistor 19 of the coupler 43. Battery 44 also supplies current to the resistance network of the thyratron anode circuit comprising resistors 20 and 21 which are shunted across a capacitor 22. The capacitor has one terminal connected to the anode of the thyratron and its other terminal to the detonator, forming a series circuit through the detonator to the filament of the thyratron. The resistor 21 prevents a charge from being built up prematurely across the capacitor 22. The operating grid of the thyratron is biased slightly below the firing point by means of a battery 23 through a resistor 24 of the coupler. Switches 25 and 26 which are operable by setback forces or by any suitable means, not shown, are connected in series with the filament battery 27 and anode battery 44, respectively.

When the projectile is fired, switches 25 and 26 operate to close the filament and anode circuits of the pentode and thyratron tubes. Closing of switch 26 also charges the capacitor 22. Since the current which charges the capacitor 22 also flows through detonator 6 as shown in FIG. 3, the detonator 6 is obviously chosen in cooperation with the capacitor 22 and the ,resistor 20 so that the detonator will not be fired when capacitor 22 is charged. Likewise, it is obvious that the resistor 21 must be chosen relative to the resistance of detonator 6 to prevent firing thereof when the switch 26 is closed. The voltage between number 2 grid and the cathode of pentode 9 will be zero in the absence of target proximity. This will place all the grids of pentode 9 at zero potential with respect to the cathode resulting in a small anode current flowing in the pentode anode circuit. When the projectile is within triggering distance of the target the potential on cap 3 becomes more negative in respect to the potential on body la as described previously. This difference in potentials is translated to the number 2 grid of the pentode causing a decrease in conduction which results in a decrease of voltage drop across resistor 19, and hence a voltage rise at the capacitor 28 and a subsequent positive pulse to the control grid of the thyratron 10 which causes the thyratron to fire. The capacitor 22 then discharges, to function detonator 6 in the booster 29 whereupon the booster detonates the explosive charge 5.

We claim:

1. In combination with an explosive missile, an electrostatic fuse comprising: a conical casing mounted at the nose end of said missile, said casing having a metal cap at its narrow end and an insulating skirt between said cap and the body of said missile whereby a capacitance C exists between said cap and said body, said cap and said body having a charge placed thereon during missile launching; a resistance R connected between said cap and said body, said resistance R thereby being in parallel with the capacitance C, the value of said resistance R being such that the time constant RC is long compared to the time the missile is within proximity of a target, but short compared to the time of flight of the missile; a pentode mounted within said missile at its nose end, said pentode having an anode, a cathode, and three grids, the number 2 grid of said pentode being connected to said cap, and the number 1 and number 3 grids of said pentode being connected to said cathode, said cathode being connected to the body of said missile, said number 2 grid thereby being shielded from both said anode and said cathode; a positive voltage source within said missile; a resistor connected between the anode of said pentode and said source; a firing circuit having a thyratron, a charged capacitor, and a detonator, said thyratron having an anode, a cathode, and a grid, said charged capacitor and detonator being connected in the anode circuit of said thyratron; and a coupling network connected between the anode of said pentode and the grid of said thyratron; the greater increase in the capacitance of said cap than that of said body upon approach of said missile to a target causing a change in the voltage across said parallel capacitance C and resistance R, this voltage change being amplified by said pentode and transferred by said coupling network to the grid of said thyratron, whereupon said thyratron conducts causing said charged capacitor to pass a current through said detonator causing functioning 

1. In combination with an explosive missile, an electrostatic fuse comprising: a conical casing mounted at the nose end of said missile, said casing having a metal cap at its narrow end and an insulating skirt between said cap and the body of said missile whereby a capacitance C exists between said cap and said body, said cap and said body having a charge placed thereon during missile launching; a resistance R connected between said cap and said body, said resistance R thereby being in parallel with the capacitance C, the value of said resistance R being such that the time constant RC is long compared to the time the missile is within proximity of a target, but short compared to the time of flight of the missile; a pentode mounted within said missile at its nose end, said pentode having an anode, a cathode, and three grids, the number 2 grid of said pentode being connected to said cap, and the number 1 and number 3 grids of said pentode being connected to said cathode, said cathode being connected to the body of said missile, said number 2 grid thereby being shielded from both said anode and said cathode; a positive voltage source within said missile; a resistor connected between the anode of said pentode and said source; a firing circuit having a thyratron, a charged capacitor, and a detonator, said thyratron having an anode, a cathode, and a grid, said charged capacitor and detonator being connected in the anode circuit of said thyratron; and a coupling networK connected between the anode of said pentode and the grid of said thyratron; the greater increase in the capacitance of said cap than that of said body upon approach of said missile to a target causing a change in the voltage across said parallel capacitance C and resistance R, this voltage change being amplified by said pentode and transferred by said coupling network to the grid of said thyratron, whereupon said thyratron conducts causing said charged capacitor to pass a current through said detonator causing functioning thereof. 